Early Embryonic Development Flashcards
_______ increase number of cells in the embryo
celavage or mitotic cell divisions
in a blastomere, stage is determined by
number of cells
what determines pattern of cleavage
yolk volume
what is yolk
protein and lipids
isolecithal ova type occurs in
most mammals (placenta/marsupials)
isolecithal characteristics
small amount of yolk, evenly distributed throughout cytoplasm
holoblastic cleavage
holoblastic cleavage
blastomeres divide completely
megalecithal animals include
egg laying mammals (platypi, echidna, spiny anteater), birds, reptiles
megalecithal characteristics
abundant yolk with embryo forming cytoplasm at the opposite end of zygote
megalecithal animal pole
embryo cytoplasm
megalecithal vegetal pole
yolk rich cytoplasm
what is meroblastic cleavage
cleavage initiated at animal pole, but large yolk mass does not divide (cell division incomplete)
meroblastic cleavage: blastodisc
small region of animal pole becomes embryo
meroblastic cleavage: yolk
food supply for developing embryo
1st cell division produces
2 daughter cells called blastomeres; 2 polar bodies visible
2nd cell division produces
4 cell stage (4 blastomeres)
3rd cell division produces
8 cell stage (8 blastomeres)
what happens to zona pellucida during these cell divisions?
it remains intact and the same size (does not increase in size as the embryo grows)
as long as zona pellucida remains, what happens to cell sizes during each cleavage
cell size decreases
what is a morula
16-32 cell stage; solid mass of cells
is the zona pellucida intact in a morula?
yes
what is the range of the length of time post-ovulation to reach uterus
2-8 days
most species time to reach uterus post-ovulation
3 days
length of time in dog for post-ovulation to reach uterus
8 days